The sacral vertebrae fuse together and with their ossified intervertebral discs, to form the sacrum, a single bone in all domestic species.
The cranial part of the sacrum (mainly first sacral vertebra) articulates cranially with the lumbar spine (lumbosacral joint at the lumbosacral vertebral junction) and with the pelvic girdle (sacroiliac joints). The caudal part of sacrum forms the roof of the pelvic cavity.
The cranial extremity of sacrum is termed the base:
The dorsal surface of sacrum presents the dorsal sacral foramina (openings for the exit of the dorsal branches of the sacral nerves) and different crests:
The pelvic surface of sacrum is the ventral surface. It presents the ventral pelvic foramina, openings for the exit of the ventral branches of the sacral nerves. The transverse lines, on pelvic surface, are the result of fused sacral bodies and indicates the former limits of the individual vertebrae.
The apex of sacrum is the small caudal extremity of sacrum, it presents a caudal articular process in carnivores and pigs.
The sacrum contains the sacral canal: it is the continuation of the vertebral canal in the sacrum (with a diameter much more narrower in the sacrum than in the lumbar region).